A biophysical model of lysozyme self-association

The concentration dependence of the self-association of hen egg-white lysozyme was studied spectrophotometrically at pH 6, 25 degrees C, and low ionic strength within a concentration range of 2.5-50 micrograms/ml. Of several possible mathematical models, an ideal or nearly ideal two-stage model representing an equilibrium between monomers and dimers and between dimers and trimers best describes the data. The dimerization and trimerization constants were found to be 2.5 x 10(-2) and 38 x 10(-2). Dialysis experiments confirmed that the mechanism involves three associating species. A "head-to-tail" contact between the associating sites was inferred from dialysis studies of the effect of indole and imidazole derivatives on lysozyme self-association.